1. Field of the Invention
The present invention relates to an improvement in a reference electrode of a silver/silver chloride electrode composition for immersion in an internal solution to serve as an internal electrode and, more particularly, to an electrode assembly capable of minimizing any blockage of a liquid junction.
2. Description of Related Art
In a reference electrode having the above-described construction, a soluble silver ion (Ag.sup.+) is dissolved from the silver/silver chloride electrode during the use of the reference electrode, or dissolved chloro complex ions are formed by the following reactions (1) and (2) listed below as equations, and the ions are brought into contact with a lower potential chloride ionized water at a liquid junction to make the above-described respective reactions progress in the left direction, whereby AgCl (silver chloride) is settled out of the solution. EQU AgCl+Cl.sup.- .revreaction.AgCl.sub.2.sup.- ( 1) EQU AgCl.sub.2.sup.- +Cl.sup.- .revreaction.AgCl.sub.3.sup.2- ( 2)
In particular during the continuous use of such a reference electrode at a high temperature of 60.degree. C. or more, the concentration of silver ion and chloro complex ion can be increased and the silver ion will be turned into silver chloride during a reduction of temperature, to eventually cause a blockage of the liquid junction. Such a reference electrode, during continuous use at 100.degree. C., will cause the liquid junction to be blocked with silver chloride within about several days. In addition, in the case where interferential substances, such as protein, silver, mercury, and H.sub.2 S, contained in a sample to be tested, enter the internal solution through the liquid junction, there is the further possibility that these interferential substances can change the electrical potential of the internal electrode, and the interferential substances may further act upon the silver ion to additionally form soluble precipitates which will also block the liquid junction.
Because of these problems, the internal solution must be periodically exchanged with a new solution to prevent the quantity of silver ions and chloro complex ions existing in the internal solution from increasing, or the internal solution must be compulsorily leaked to prevent the sample being tested from being sucked up due to any change in pressure resulting from a temperature cycle and the like.
However, exchanging the internal solution does not effectively remove silver ions, which are a dominant cause of the blockage of the liquid junction, and maintenance problems are also created in making such exchanges. In addition, the latter measure has shown disadvantages in that the reference electrode is complicated in construction, expensive, and becomes ineffective during continuous use.